Okay another hypothetical. Say that the defendant can prove without a doubt that at the time of purchasing/filling out his 4473, he had never engaged in a federally controlled substance, yet since then he engaged in SD homicide and had smoked weed 2 weeks prior?

For instance a 50 year old man in Colorado bought an 870 in the 80s, yet since it was legalized in his state he tried it for the first time. Then a couple weeks later an intruder threatens his life and he reacts?

__________________
I told the new me,
"Meet me at the bus station and hold a sign that reads: 'Today is the first day of the rest of your life.'"
But the old me met me with a sign that read: "Welcome back."
Who you are is not a function of where you are. -Off Minor